1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
|
%
% Tutorials / bi-quad antenna
%
% Tested with
% - Octave 3.8.1
% - openEMS v0.0.32
%
% (C) 2011-2014 Thorsten Liebig <thorsten.liebig@uni-due.de>
close all
clear
clc
%% setup the simulation
physical_constants;
unit = 1e-3; % all length in mm
quad_size = 110;
port_length = 10;
quad_mesh = 5;
Feed_R = 75;
% size of the simulation box
SimBox = [800 800 400];
% frequency range of interest
f_start = 400e6;
f_stop = 1000e6;
% frequency of interest
f0 = 700e6;
freq = linspace(f_start,f_stop,201);
%% setup FDTD parameter & excitation function
FDTD = InitFDTD( 'endCriteria', 1e-4 );
FDTD = SetGaussExcite(FDTD,0.5*(f_start+f_stop),0.5*(f_stop-f_start));
BC = {'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8'}; % boundary conditions
FDTD = SetBoundaryCond( FDTD, BC );
%% setup CSXCAD geometry & mesh
CSX = InitCSX();
%create fixed lines for the antenna outline and port
mesh.x = [-quad_size*sqrt(2) -quad_size/sqrt(2) 0 quad_size/sqrt(2) quad_size*sqrt(2)];
mesh.y = [-quad_size/sqrt(2) -port_length/2 0 port_length/2 quad_size/sqrt(2)];
mesh.z = [0];
mesh = SmoothMesh(mesh, quad_mesh, 1.3);
% add air box
mesh.x = [mesh.x -SimBox(1)/2 SimBox(1)/2];
mesh.y = [mesh.y -SimBox(2)/2 SimBox(2)/2];
mesh.z = [-SimBox(3)/2 0 SimBox(3)/2];
max_res = c0 / (f_stop) / unit / 20; % cell size: lambda/20
mesh = SmoothMesh(mesh, max_res, 1.4);
CSX = DefineRectGrid( CSX, unit, mesh );
%% create bi-quad
points(1,1) = 0;
points(2,1) = port_length/2;
points(3,1) = 0;
points(1,end+1) = quad_size/sqrt(2);
points(2,end) = quad_size/sqrt(2);
points(1,end+1) = quad_size*sqrt(2);
points(2,end) = 0;
points(1,end+1) = quad_size/sqrt(2);
points(2,end) = -quad_size/sqrt(2);
points(1,end+1) = 0;
points(2,end) = -port_length/2;
points(1,end+1) = -quad_size/sqrt(2);
points(2,end) = -quad_size/sqrt(2);
points(1,end+1) = -quad_size*sqrt(2);
points(2,end) = 0;
points(1,end+1) = -quad_size/sqrt(2);
points(2,end) = quad_size/sqrt(2);
points(1,end+1) = 0;
points(2,end) = port_length/2;
% create a thin metal wire...
CSX = AddMetal(CSX,'metal'); %create PEC with propName 'metal'
CSX = AddCurve(CSX,'metal',10, points);
%% apply the excitation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
start = [0 -port_length/2 0];
stop = [0 port_length/2 0];
[CSX port] = AddLumpedPort(CSX,10,0,Feed_R,start,stop,[0 1 0], true);
%% nf2ff calc
start = [mesh.x(9) mesh.y(9) mesh.z(9)];
stop = [mesh.x(end-8) mesh.y(end-8) mesh.z(end-8)];
[CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', start, stop);
%% prepare simulation folder
Sim_Path = 'tmp';
Sim_CSX = 'bi_quad_ant.xml';
[status, message, messageid] = rmdir( Sim_Path, 's' ); % clear previous directory
[status, message, messageid] = mkdir( Sim_Path ); % create empty simulation folder
%% write openEMS compatible xml-file
WriteOpenEMS([Sim_Path '/' Sim_CSX], FDTD, CSX);
%% show the structure
CSXGeomPlot([Sim_Path '/' Sim_CSX]);
%% run openEMS
RunOpenEMS(Sim_Path, Sim_CSX);
%% postprocessing & do the plots
port = calcPort(port, Sim_Path, freq);
s11 = port.uf.ref ./ port.uf.inc;
% plot reflection coefficient S11
figure
plot( freq/1e9, 20*log10(abs(s11)), 'k-', 'Linewidth', 2 );
ylim([-30 0]);
grid on
title( 'reflection coefficient S_{11}' );
xlabel( 'frequency f / GHz' );
ylabel( 'reflection coefficient |S_{11}|' );
%% calculate 3D far field pattern
phiRange = -180:2.5:180;
thetaRange = 0:2.5:180;
nf2ff = CalcNF2FF(nf2ff, Sim_Path, f0, thetaRange*pi/180, phiRange*pi/180);
disp( ['directivity: Dmax = ' num2str(10*log10(nf2ff.Dmax)) ' dBi'] );
% plot far-field pattern with Matlab
figure
plotFF3D(nf2ff, 'logscale', -20)
%%
disp( 'Dumping far-field pattern to vtk (use Paraview to visualize)...' );
DumpFF2VTK('Bi_Quad_Pattern.vtk', nf2ff.E_norm{1} / max(nf2ff.E_norm{1}(:)) * nf2ff.Dmax, thetaRange, phiRange, 'scale', 0.05);
|
